1. Field of the Invention
This invention relates to an abrasive tape for use in polishing of a magnetic head for a magnetic recording and reproducing apparatus. This invention particularly relates to an abrasive tape for use in polishing of a magnetic head mainly by being moved between two reels.
2. Description of the Prior Art
Video or high grade audio magnetic heads are required to have very smooth tape sliding surfaces. Therefore, in general, in the process of making the magnetic head, the magnetic head is disposed at a predetermined position after being rough ground, and the tape sliding surface of the magnetic head is polished to a smooth finish by moving an abrasive tape between two reels disposed with the magnetc head intervening therebetween. In general, the abrasive tape comprises a flexible substrate, and a coating film formed on the flexible substrate by applying an abrasive composition containing fine abrasive grains, a binder, and optionally an additive such as a lubricant, which are kneaded together, onto the flexible substrate. Since the abrasive tape is flexible and can therefore snugly fit to the curved surface of the tape sliding surface of the magnetic head, it can polish the surface accurately.
As the abrasive tape, there has heretofore been known, for example, a cleaning tape as disclosed in Japanese Unexamined Patent Publication No. 53(1978)-102017, which comprises a substrate, and a coating film overlaid on the substrate by applying thereonto an abrasive composition containing, for example, abrasive grains consisting of zinc oxide (ZnO), a binder consisting of a vinyl chloride-vinyl acetate copolymer, a polyester polyol or a polyisocyanate, and various additives, for example, a lubricant such as silicone oil, which are kneaded together.
Accordingly, it is considered to replace only the abrasive grains by a substance harder than zinc oxide in the aforesaid cleaning tape and to use the tape thus obtained as an abrasive tape.
However, with the abrasive tape formed by using the vinyl chloride-vinyl acetate copolymer or the polyester polyol as the binder, dispersibility of the abrasive grains by the vinyl chloride resin is low, and the abrasive grains often agglomerate and concentrate locally in the abrasive tape, thereby causing scratching of the polished surface.
On the other hand, in recent years, magnetic heads formed of Permalloy are used widely as, for example, audio magnetic heads. However, Permalloy is a soft and readily corrodible alloy, and therefore the tape sliding surface of the Permalloy magnetic head is readily corroded. With the abrasive tape formed by using the vinyl chloride-vinyl acetate copolymer as the binder, hydrochloric acid is readily released from the binder and corrodes the polished surface contacting the abrasive tape. Therefore, the abrasive tape formed by using the vinyl chloride resin as the binder is not suitable particularly in the case where the material which is to be polished is readily corrodible as in the case of the Permalloy magnetic head.
Also, abrasive tapes are required to exhibit substantially high durability of the abrasive layer. In the case where durability of the abrasive layer is low and the abrasive grains readily separate from the abrasive layer, the abrasive grains accumulate between the abrasive tape and the polished surface, thereby scratching the polished surface.